Author Topic: Measuring water in a water tank  (Read 19556 times)

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Offline ilium007

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Measuring water in a water tank
« on: January 06, 2013, 03:01:36 am »
Hi - I have been on this little project for a few years on and off with no success. I would like to measure water in my 25,000l water tanks at home and use the data to track water usage, quantity and also possible to switch on some transfer pumps.

I have looked at commercial pressure transducers - these are prohibitively expensive (I have 5 tanks to measure)

I have looked at homebrew pressure differential projects - the sensors available will not allow water to come in contact with the pressure sensor surface.

I have looked at capacitance sensors but these seem to be quite susceptible to temperature as well and may not be accurate enough for my needs.

I have purchased a Maxbotix sensor that uses ultrasonic waves to sense objects - I have played around with this a lot on the Arduino platform and it could be useable but I dont yet know how accurate it will be, the results are very dependent on temperature. 1cm in my tanks equates to about 70l of water. This would be about the accuracy I am after.

The only thing left to look into is a hall effect based sensor array with a floating magnetic device. I am thinking I could have a tubular pole inside the tank (approx 2m high)  with a bunch of hall effect sensors placed equally inside. as the float moves up the pole various sensors will be triggered and I can interpret on the arduino. I dont know how I would get a string of them interconnected, I dont know how I would interface xx number of sensors top the arduino (limitied input pins) and I dont know how far to space the sensors apart so that the magnet does not interfere with the sensor above and below. I know that I can not have a sensor for every 1cm of water depth so I would need some way of interpreting the magnet sitting between two sensors.

Any thoughts on how to measure water in a tank would be greatly appreciated.
 

Offline 8086

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Re: Measuring water in a water tank
« Reply #1 on: January 06, 2013, 03:28:17 am »
Perhaps sonar? Affixed to the inside of the top of the tank? Will reflect off the water and the delay will give you the level.
 

Offline UPI

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Re: Measuring water in a water tank
« Reply #2 on: January 06, 2013, 03:38:31 am »
An auto-retracting reel of fishing line (just enough tension to remove string slack) with a float at the end monitored with an encoder on the reel.
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #3 on: January 06, 2013, 03:54:35 am »
Perhaps sonar? Affixed to the inside of the top of the tank? Will reflect off the water and the delay will give you the level.

Yes - this is the Maxbotix sensor that I have trialed. One of the biggest issues with this approach is that the speed of sound varies with temperature and inside a water tank it could be 35 - 40 degrees during the day (the air gap between the top of the water and the top of the inside of the tank) and down as low as 15 degrees of a night time.
« Last Edit: January 06, 2013, 03:59:07 am by ilium007 »
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #4 on: January 06, 2013, 03:57:04 am »
An auto-retracting reel of fishing line (just enough tension to remove string slack) with a float at the end monitored with an encoder on the reel.

I had thought of this one as well but moved away from the idea of mechanical devices that could fail. I had thought of a loop of wire on two pulleys turning a rotary encoder. Even reusing a commercially available water tank gauge (the one with the float indicator on the outside of the tank) by putting a rotary encoder on the pulley - someone said to me that this combination of mechanical devices was a bad idea.
 

Offline 8086

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Re: Measuring water in a water tank
« Reply #5 on: January 06, 2013, 04:02:48 am »
Perhaps sonar? Affixed to the inside of the top of the tank? Will reflect off the water and the delay will give you the level.

Yes - this is the Maxbotix sensor that I have trialed. One of the biggest issues with this approach is that the speed of sound varies with temperature and inside a water tank it could be 35 - 40 degrees during the day (the air gap between the top of the water and the top of the inside of the tank) and down as low as 15 degrees of a night time.

Oh. I must have skipped over that part of your post.

Could you have a simple temperature sensor in there too, and compensate?
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #6 on: January 06, 2013, 04:04:58 am »
Perhaps sonar? Affixed to the inside of the top of the tank? Will reflect off the water and the delay will give you the level.

Yes - this is the Maxbotix sensor that I have trialed. One of the biggest issues with this approach is that the speed of sound varies with temperature and inside a water tank it could be 35 - 40 degrees during the day (the air gap between the top of the water and the top of the inside of the tank) and down as low as 15 degrees of a night time.

Oh. I must have skipped over that part of your post.

Could you have a simple temperature sensor in there too, and compensate?

I do have a temp sensor but here is the problem.... where do you put it inside the tank (between the sensor and water) so that when the tank is filling the sensor is not under water ?
 

Offline UPI

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Re: Measuring water in a water tank
« Reply #7 on: January 06, 2013, 04:12:16 am »
I had thought of this one as well but moved away from the idea of mechanical devices that could fail.

How would you feel about a motor lowering a continuity sensor into the tank?
 

Offline 8086

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Re: Measuring water in a water tank
« Reply #8 on: January 06, 2013, 04:15:13 am »
Perhaps sonar? Affixed to the inside of the top of the tank? Will reflect off the water and the delay will give you the level.

Yes - this is the Maxbotix sensor that I have trialed. One of the biggest issues with this approach is that the speed of sound varies with temperature and inside a water tank it could be 35 - 40 degrees during the day (the air gap between the top of the water and the top of the inside of the tank) and down as low as 15 degrees of a night time.

Oh. I must have skipped over that part of your post.

Could you have a simple temperature sensor in there too, and compensate?

I do have a temp sensor but here is the problem.... where do you put it inside the tank (between the sensor and water) so that when the tank is filling the sensor is not under water ?

Depends just how much the temperature difference between top and bottom of the tank is an issue. I would expect the air temperature to be uniform enough at any given time to be able to make a fairly accurate temp compensated measurement. So it would appear your options would be to either have it at the top (with the transducer), or on a float.
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #9 on: January 06, 2013, 04:17:07 am »
I had thought of this one as well but moved away from the idea of mechanical devices that could fail.

How would you feel about a motor lowering a continuity sensor into the tank?

Thats back to a mechanical based measuring approach. What I would l really love to do is investigate this hall effect idea further. Nothing to break / go wrong. My idea is that I should get a predictable fall off of voltage through the sensor as the magnet moves closer and farther away from the sensor, thus when a magnet is right near a sensor it will allow, say, a full 5V, as the magnet moves further from one sensor the voltage will drop but then start rising on the next sensor until it is at 5V and the other sensor is at 0v. Thats the idea anyway !
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #10 on: January 06, 2013, 04:18:13 am »
Quote
or on a float.

Now thats an idea !
 

Offline Jimmy

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Offline ilium007

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Re: Measuring water in a water tank
« Reply #12 on: January 06, 2013, 04:38:12 am »
Are you serious !!!! When did these come into stock !!
 

Online chickenHeadKnob

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Re: Measuring water in a water tank
« Reply #13 on: January 06, 2013, 04:44:06 am »
Hi - I have been on this little project for a few years on and off with no success. I would like to measure water in my 25,000l water t
The only thing left to look into is a hall effect based sensor array with a floating magnetic device. I am thinking I could have a tubular pole inside the tank (approx 2m high)  with a bunch of hall effect sensors placed equally inside. as the float moves up the pole various sensors will be triggered and I can interpret on the arduino. I dont know how I would get a string of them interconnected, I dont know how I would interface xx number of sensors top the arduino (limitied input pins) and I dont know how far to space the sensors apart so that the magnet does not interfere with the sensor above and below. I know that I can not have a sensor for every 1cm of water depth so I would need some way of interpreting the magnet sitting between two sensors.

Any thoughts on how to measure water in a tank would be greatly appreciated.

OK what I have to offer is somewhat physically similar to your hall sensor string but much simpler and cheaper. A pipe or tube constrains a float to only vertical travel. Float supports a precisely notched ruler, or plastic stick with reflective and dark bands like a ruler, but I think notches are easier. I would make it out of acrylic or aluminum. At the top, in free air, the ruler ticks would be read by optical interrupter. Two or more interrupters and corresponding index holes in the stick let you do limit detect or you can calibrate once and hope your micro never loses count. Disadvantage is that you have to accommodate  vertical travel of the ruler above the tank when it is full. Easy to get 1 to 5 mm accuracy.
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #14 on: January 06, 2013, 04:45:39 am »
Hi - I have been on this little project for a few years on and off with no success. I would like to measure water in my 25,000l water t
The only thing left to look into is a hall effect based sensor array with a floating magnetic device. I am thinking I could have a tubular pole inside the tank (approx 2m high)  with a bunch of hall effect sensors placed equally inside. as the float moves up the pole various sensors will be triggered and I can interpret on the arduino. I dont know how I would get a string of them interconnected, I dont know how I would interface xx number of sensors top the arduino (limitied input pins) and I dont know how far to space the sensors apart so that the magnet does not interfere with the sensor above and below. I know that I can not have a sensor for every 1cm of water depth so I would need some way of interpreting the magnet sitting between two sensors.

Any thoughts on how to measure water in a tank would be greatly appreciated.

OK what I have to offer is somewhat physically similar to your hall sensor string but much simpler and cheaper. A pipe or tube constrains a float to only vertical travel. Float supports a precisely notched ruler, or plastic stick with reflective and dark bands like a ruler, but I think notches are easier. I would make it out of acrylic or aluminum. At the top, in free air, the ruler ticks would be read by optical interrupter. Two or more interrupters and corresponding index holes in the stick let you do limit detect or you can calibrate once and hope your micro never loses count. Disadvantage is that you have to accommodate  vertical travel of the ruler above the tank when it is full. Easy to get 1 to 5 mm accuracy.

Nice idea - I will look into that further.
 

Offline NiHaoMike

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Re: Measuring water in a water tank
« Reply #15 on: January 06, 2013, 05:01:37 am »
Maybe use some waterproof wire (a piece backed onto itself and then lowered vertically into the tank) and sense the capacitance between it and the tank?

Or use sonar from the bottomside along with a temperature sensor. Water conducts (and stores) heat very well so there shouldn't be very much of a temperature difference between the top and bottom of the water.

There are also infrared distance sensors available.

Or couple a speaker and microphone to the top of the tank and measure the resonant frequency of the airspace.

If a low resolution digital readout is fine, you could attach some heaters (metal cased power resistors work great) and temperature sensors (common NTCs work fine) to several levels on the outside of the tank. (Immersing them inside the tank also works, but waterproofing it requires more work.) First do a temperature readout without the heaters, then switch the heaters on for some time (say a few minutes), then take another readout. The parts of the tank that are covered by water would not change temperature very much, while the parts that are not covered would get significantly hotter. (I remember reading about a car that used a PTC to signal a light when the oil level is starting to run low.)
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Offline SeanB

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Re: Measuring water in a water tank
« Reply #16 on: January 06, 2013, 05:28:18 am »
5 washing machine pressure sensors ( the newer ones used in digitally controlled machines) and have the 4069 oscillator next to it in the box at the top of the tank. Feed the square wave back to the central point using Cat5 cable, 2 pairs for power and 1 pair for a differential signal, easy enough to arrange with 5 spare oscillators. 2 in parallel as bus drivers works for each line via a 100R resistor. Then you measure frequency and convert it to level. They are pretty consistent and ultra cheap, especially if you go out on scrap day or to the scrappie and ask for 5 machines as they come in.

Oscillator is part of the schematic, even gives the values and the frequency ranges.
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #17 on: January 06, 2013, 05:51:17 am »
5 washing machine pressure sensors ( the newer ones used in digitally controlled machines) and have the 4069 oscillator next to it in the box at the top of the tank. Feed the square wave back to the central point using Cat5 cable, 2 pairs for power and 1 pair for a differential signal, easy enough to arrange with 5 spare oscillators. 2 in parallel as bus drivers works for each line via a 100R resistor. Then you measure frequency and convert it to level. They are pretty consistent and ultra cheap, especially if you go out on scrap day or to the scrappie and ask for 5 machines as they come in.

Oscillator is part of the schematic, even gives the values and the frequency ranges.

I wish I know what an oscillator did ! But I dont ! Was there supposed to be a schematic linked ? Also, what effect does temperature have on an oscillator ?
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #18 on: January 06, 2013, 06:53:17 am »
Or you could just get a bit of rope and a pulley (or two). Attach a float to one end and a weight to the other. My uncle used a couple of jam jars with a hole in the center of the lid through which he passed the rope and tied a knot. As the water level goes one way the weight goes the other. It may be mechanical but it sure isn't unreliable. My uncle rigged his up long before you could buy electrical gizmos. It worked for decades. He "may" have had to lubricate the pulley but it was hardly enduring a hard life.

In some parts of the world simple mechanical devices are considered desirable solutions to problems.

Anyone could see the level at a glance.

If you absolutely must electrify it you could have the weight pass a series of photo diodes and detect the light level change. Say run the weight inside a PVC pipe with a series of detectors and holes along its length. Or micro switches or reed switches with a magnet on the weight.

If you want to know the consumption rate of water then I suggest a flow sensor in the outlet pipe would be better . I think knowing the tank level to 10% is sufficient for most people.

10% is 2500l that is less than the amount I need between calling the water man (we dont have town water) and running out of water. The other reason to measure water level is to pump out of a 5000l sump tank into the 25000 tanks during rain sessions. I want to be able to measure the water level in this tank accurately so that I can estimate the rate of water coming down out of the sky.

And I want to do it electronically because this is a hobby and a hobby is about learning stuff. I could go and poke a stick in the tank every day but where is the fun in that ??
 

Offline ilium007

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Re: Measuring water in a water tank
« Reply #19 on: January 06, 2013, 07:03:31 am »
So how about something like:



With a decent rotary encoder mounted up the top:



Then all I need is code the arduino to suit.
« Last Edit: January 06, 2013, 07:05:17 am by ilium007 »
 

Offline firewalker

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Re: Measuring water in a water tank
« Reply #20 on: January 06, 2013, 07:56:22 am »
Years ago I had use a multi turn top. I had mounted a pulley and a
with string and a floating weight on the other end. It was working quite nicely.

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Offline Kremmen

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Re: Measuring water in a water tank
« Reply #21 on: January 06, 2013, 10:50:09 am »
One traditional method, much used in the industry, is to measure the fluid column pressure using a simple air pipe. Just run a hose or tube to the bottom of the tank - open from the bottom, sealed from the top. Attach one of these http://www.digikey.com/product-search/en/sensors-transducers/pressure/1966259?k=pressure%20sensor to the sealed top and process the result as you need.
No moving parts, measures anything from pure water to septic waste, virtually foolproof. The only precaution would be to have some kind of air valve, maybe a car tire type, for flushing the pipe in case of a leak.
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Offline ilium007

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Re: Measuring water in a water tank
« Reply #22 on: January 06, 2013, 10:51:59 am »
One traditional method, much used in the industry, is to measure the fluid column pressure using a simple air pipe. Just run a hose or tube to the bottom of the tank - open from the bottom, sealed from the top. Attach one of these http://www.digikey.com/product-search/en/sensors-transducers/pressure/1966259?k=pressure%20sensor to the sealed top and process the result as you need.
No moving parts, measures anything from pure water to septic waste, virtually foolproof. The only precaution would be to have some kind of air valve, maybe a car tire type, for flushing the pipe in case of a leak.

I had considered this as well, but the major drawback is during the day, when the sun heats the air in the pipe, the air expands and exerts pressure on the sensor causing inaccurate readings.

A real differential pressure sensor such as this:



sells for approx $500 US - way out of my budget considering I have 5 tanks to do.
« Last Edit: January 06, 2013, 11:00:20 am by ilium007 »
 

Offline peter.mitchell

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Re: Measuring water in a water tank
« Reply #23 on: January 06, 2013, 10:58:36 am »
One traditional method, much used in the industry, is to measure the fluid column pressure using a simple air pipe. Just run a hose or tube to the bottom of the tank - open from the bottom, sealed from the top. Attach one of these http://www.digikey.com/product-search/en/sensors-transducers/pressure/1966259?k=pressure%20sensor to the sealed top and process the result as you need.
No moving parts, measures anything from pure water to septic waste, virtually foolproof. The only precaution would be to have some kind of air valve, maybe a car tire type, for flushing the pipe in case of a leak.

I had considered this as well, but the major drawback is during the day, when the sun heats the air in the pipe, the air expands and exerts pressure on the sensor causing inaccurate readings.

don't put the pipe in the sun?
 

Offline Kremmen

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Re: Measuring water in a water tank
« Reply #24 on: January 06, 2013, 10:59:20 am »
OK. the pipe is open from the bottom so any expanding air will escape and the reading won't change because of that. But the situation changes when the system cools down and the air contracts. Then you do get a measuremnent error because the pipe is not completely air filled any more. What they do in this case is to set up a bubbler that slowly pushes air into the pipe, letting it escape from the bottom. That way the system is not dependent on temp variations. Could still be the cheapest solution provided you can find a suitable pump... If the accuracy is sufficient, i would say this merits serious consideration due to its simplicity. There must be a reason why it is/was so common in the industry.

P.S. why would you want to use an expensive pressure transmitter like the image you attached? That is not comparable to the other solutions where you would be building the system yourself. The sensor components i linked are just a few bucks a piece.
« Last Edit: January 06, 2013, 11:06:46 am by Kremmen »
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